Adsorption of pyrimenthanil on soil and some of its colloids

The adsorption of pyrimethanil (PYR) on two soils and on some soil components (kaolinite, vermiculite, smectite, humic acids, and ferrhydrite), were studied by means of batch technique. In addition, adsorption experiments were carried out with two portions of humin, defined as additional organic matter, isolated from a soil. A preliminary study demonstrated that PYR has a high affinity for smectite and humic acid indifferently of whether the pure or commercial product was used (adsorption of more than 85% in all tests), while it showed little affinity for kaolinite or ferrihydrite (adsorption of less than 6%) and an intermediate affinity for vermiculite (adsorption of about 23%). In soils the fungicide demonstrated a greater affinity at lower concentrations (‘L’ type isotherms) and was more greatly adsorbed by soil with a high organic carbon content. PYR had an ‘S’ type isotherm in all the humic substances isolated. Nevertheless, adsorption was very high at both high and low concentrations, with greater values being found for the additional organic matter than for the humic acid. Little is known about the adsorption of xenobiotis on humin. Our results highlighted the important role of this portion of organic matter in the adsorption of organic compounds. The results obtained showed that pyrimenthanil is not very mobile in the soil and therefore, there is very little risk of it polluting groundwater.